1. Field of the Invention
This invention is a further development in high-vacuum technology, particularly with respect to hydrogen outgassing and pumping.
2. Description of the Prior Art
In a discussion of the state of the art appearing in The Journal of Vacuum Science and Technology, Vol. 6, No. 1, January/February 1969, pp. 166-173, the author, D.G. Bills, concluded: " . . . present day vacuum systems have ultimate pressure limited not by any failure of the pumping mechanism, but by inadequate or improper processing of the system materials. This limitation appears to be due to diffusion of dissolved gases, mainly hydrogen, out of only partially degassed portions of the systems." The rate of permeation of hydrogen through stainless steels at 371.degree.C is in the order of 5.times.10.sup.-.sup.3 cc(STP)mm/hr/cm.sup.2 /atm.sup.0.5. It is known with respect to stainless steels, from which a major share of the components of a vacuum system are typically made, that an oxide layer on the surface of such a stainless steel component serves to decrease the rate of hydrogen permeation through the surface by a factor of 10.sup.3 as compared to an untreated surface. However, such oxide layers are generally nonadherent or only poorly adherent to stainless steel surfaces.
A substance known in brazing practice as "green oxide" or "chrome oxide" adheres readily to stainless steels. This substance, which will hereinafter be described more definitively, is formed as an adherent coating on brazing jigs to prevent brazing alloys from sticking to the jig surfaces. However, the so-called "green oxide" has not heretofore been used as a hydrogen diffusion barrier in high-vacuum technology because of the extremely high heat of adsorption of water on the "green oxide", about 30,000 calories per mole. The high affinity for water vapor in the ambient atmosphere that is exhibited by oxides which are adherent to stainless steels has inhibited the use of such oxides in high-vacuum applications because the water adsorbed by such oxides establishes a high partial pressure of water vapor in the vacuum system.